As the aforementioned environment, for example, a transporting system, etc., which is installed in a semiconductor manufacturing plant, may be exemplified, however, under such environment, if a grease will be used as lubricant for the driving screw, an inconvenient drawback, such as a deterioration of the lubricating property or contamination in the operational environment, may be caused according to an evaporation of an oily component from the grease.
Under such circumstances, hitherto, at least either part in moving faces of screw stem and nut, or surface of ball, is conventionally coated with a solid lubricant, such as soft metal, which includes gold, silver, lead, copper, etc., carbon, and molybdenum bisulfide in a form of film.
In the case of using the coating film made of the above mentioned solid lubricant, a dusting caused by a slight slipping of the lubricant film due to rolling and sliding motion of the ball, may be reduced to a lower level, compared with the case where grease is used, however, in which case said level is still in considerably inadequate level, particularly under the clean environment. In particular, under heavier load condition, a dusting amount is remarkably increased.
Besides these, the present invention has been carried out in coating solid lubricant, in which fluoride resin is mixed with a binder, onto at least one of sliding face between screw stem and nut, and a surface of the ball. In this case, a dusting amount may be significantly reduced compared with the above discussed conventional case.
However, even in said coating film above, dusting due to wear, other than spalling and falling of the lubricant, is remarkably increased under the relatively heavy axial load condition, resulting in shortening of the dusting life. Furthermore, if spalling and falling of the lubricating film are occurring, a lubricating function at rolling and sliding sites may be deteriorated, thereby causing trouble with respect to the operable life, such as being liable of causing adhesion due to contact between metallic parts, and accelerating abrasive wear, as well, whereas, in the environment wherein corrosive gas is present, each constitutional element, which causes spalling and falling of the lubricating film, may be attacked.
Accordingly, an object of the present invention is to provide suppressing dusting and improving in lubricating property of the driving screw, resulting in prolonging life thereof.